This disclosure relates to a trap canister mounted on a vehicle such as an automobile. In particular, it relates to a trap canister for adsorbing fuel vapor contained in a breakthrough gas discharged from a main canister configured to adsorb the fuel vapor. Here, the term “breakthrough gas” refers to gas discharged from the main canister filled with adsorbent and containing the fuel vapor leaked from the main canister in this disclosure.
In general a conventional trap canister has a hollow case where one end is open to the atmosphere and the other end is configured to introduce the breakthrough gas thereinto. The case therein defines an adsorption chamber filled with an adsorbent capable of adsorbing and desorbing the fuel vapor contained in the breakthrough gas. This breakthrough gas is discharged from a main canister configured to adsorb fuel vapor (see Japanese Laid-Open Patent Publication No. 2005-35812).
With respect to the conventional trap canister, air discharged from the main canister flows through the adsorption chamber in the trap canister during refueling. Since the adsorption chamber of the trap canister is filled with the adsorbent, the trap canister causes airflow resistance and thus high-pressure loss. This results in increased difficulty in refueling. Therefore, there has been a need for improved trap canisters.